I suppose it should be obvious that when searching for an angel in a fashion-hotel, the first place to look should be the penthouse.

And so it is. Right at the very top of a glossy, hushed high-rise edifice filled with monochrome shiny surfaces and lighting dim enough to obscure the faces of the non-beautiful, is a light-filled room housing supermodel Jordan Dunn.

OK, so technically Dunn isn't an angel in the official, branded sense. Yes, she's modelled for Victoria's Secret, but has not, unlike say, Adriana Lima and Alessandra Ambrosio, been named one of their official, Victoria's Secret Angel spokes-models. But still, at that level of elite performance in the arena of professional attractiveness, it's a case of splitting hairs. She is one tiny group of genetically perfect models who have embraced self-marketing in the social networking age. She is the 10th highest paid model in the world and is the face of Maybelline New York cosmetics. Maybe it's Maybelline? In Jourdan's case, it's quite clear that she was born with it.

She's perched on a couch in the penthouse, and preceded by a long, courtly reception-line of flunkies and minders. She unbends to stand as I enter the room and the effect is definitely of the appearance of a celestial apparition. She is very, very tall and very, very polished. But the smile is cool, or perhaps even a little tense. There is no pretence that we are settling down for a cosy chat. This is work, and though just 24, Dunn knows how to do professionalism.

The mobile phone company HTC know this. They also know that as a fashion maven who is besties with Cara Delevingne and has 1.2 million followers on Instagram, she has rare and powerful sway with the coveted youth market. Which is clearly who they are going after with their latest high-profile campaign HTC INK - which includes the release of a limited-edition version of their HTC One M9, an engraved handset which celebrates all things body art. For this, Jourdan has created her own body-art design (a hamsa hand for protection) for the phone with the help of Rihanna's own go-to tattoo-artist, Cally-Jo. She's also planning to use the design for her next tattoo. The phone is so exclusive it will not be available for purchase.

Jourdan's 'customised ink' HTC One M9 is the first of a series of celebrity designed bespoke special edition HTC One series phones.

Followers of Jourdan will know that she's into body-art. They will have seen the Instagram photos recording the day she and Cara got matching "DD" tattoos. (For Dunn and Delevingne, one imagines). They'll also be familiar with the one on the side of her hand that records her son's name in permanent ink. "All of my art on my body is very meaningful to me," she explains, when I ask her to talk me through it. "So I thought 'right, OK, I might as well get my son's name. So I got that done in Miami." But the rest, she says, is private.

"For me personally, body art is kind of personal. So I don't really like explaining what all of them mean to me. But I don't mind saying about my son's name," she hesitates for a second before deciding. "And that's it."

Dunn speaks loudly and assertively with a staccato delivery which is still recognisably 'London' despite her international career. Ever had any tattoos that she's later regretted? "One of my life mottos is to not have any regrets," she says breezily, "So no, I don't regret any of them,"

From looking at their Instagram pages, featuring splendid frocks at Cannes and sunlight in their hair at Coachella, it would be easy to imagine that life for the small group of young women in Jourdan's position is one long tampon-ad of fabulous clothes and frolicking at festivals. But to assume this would be to underestimate the women behind the images. Behind the emojis and gurning selfies, there's a very adult, grown-up side to these girls. Take Cara, for example, a fierce non-traditionalist who eschews the glittery prettiness the VS Angels project, is openly bi-sexual and bravely spoke in Vogue last month about her battle with depression.

And Jourdan is no stranger to adversity herself. She got pregnant in 2009 when just 18 years of age. Instead of motherhood signalling the death of her career, it's had the opposite effect - she appeared on the catwalk at six months gone in a specially-designed outfit by Jean Paul Gaultier which showed off her growing bump. Having initially felt a bit ambivalent about modelling, she threw herself into it with focus and determination once her son was born. The fact that Riley, now five, suffers from a painful and debilitating health condition, sickle cell anaemia, no doubt fuels her ambition further.

"One hundred percent - I now am doing this for my son," says Dunn, who is no longer in a relationship with Riley's father. "Before I had my son I was just doing it because, 'OK, I can go out and buy a really nice bag and I can go out on the weekend.' But now, I'm thinking about the fact that I can set myself up for life and Riley for school. I just view things differently. And especially, like, there's a lot of politics that goes on in the fashion industry, with shows and rejection, and people take that so seriously. For me, my son's health and caring for him is my main priority. And it kind of just weighs up what's really important."

She's been an outspoken critic too, of the lack of diversity in the fashion industry, once saying in an interview, "I don't know why people applaud designers for having just one ethnic model," although she says today that she feels optimistic about how things are changing.

"When I went back to modelling after having my son, I noticed that there were definitely more girls of colour on the runway and also in the ad campaigns as well. Before it never really used to be like that. There is a slight change. It's slowly getting there," she says.

Dunn was scouted in the Hammersmith Primark at the age of 14. She grew up in Greenford, London with her mother Dee, a receptionist and like Jourdan, a hard-working single parent. Does she, I wonder, sometimes feel that her responsibilities as a single-mother set her apart from the lifestyles all her peers are living?

"To be honest, I know I am a single mum, but I don't actually view myself as a single mum," she says. "Same with my mum, she was a single parent but she didn't really view herself as a single parent, because she had such great support from her grandmother and her mother. And that's the same with me. So I never really looked at my situation and thought, 'I have a disadvantage because I'm a single parent and because, you know, I was young when I had my child and because of work'. I didn't really see it like that."

Her mum's attitude when she was growing up was "just get on with things. Sh*t happens and you just have to carry on and just make it work.

"So I've always had that kind of view of things. There have been times when I could of just like, 'Oh my god, be down in the dumps and have a dark moment?' but I have to move on, things happen, cloudy days etc and then there will be a sunshine."

This view seems to apply to how she copes too with her son's condition. Sickle cell anaemia is an inherited blood-disorder which causes episodes of severe pain.

She's an active campaigner on behalf of sufferers. "To help spread more awareness." Eventually she wants to build "a foundation and make sure that people have got the right information and make sure that the patients have the right support and healthcare. All of that stuff is really important to me, and that's, like, my main focus"

She was initially a rather reluctant supermodel. Now, she's grateful to have made such close allies (like Cara) in the sometimes disorientating world of high fashion. Especially since, in her early working days she felt like a fish out of water.

"I remember when I first started and getting thrown in at the deep end - travelling on your own at 16 and living in a models' apartment by yourself with models from all over the world, it's a bit like, 'uurgh'.

"And for me, I didn't really think that I would be able to relate to any of these girls, but in fact we actually do have a lot in common because we are in the same boat - we're away from our friends and family, and we're going on castings, getting rejected and doing this and that, and so you kind of get bonded."